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ATC Guide mode in crevasse haul system?

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Is there a problem with using an ATC in guide mode at the anchors instead of a pulley and prussik to build the hauling system in a z-pulley?

Is it too much friction?

Won't the ATC in guide mode also capture progress as well as a pulley/prussik?

It seems simpler but no one seems to teach it so I am interested in why.

Forgive me if this is already covered someplace else.

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It works just fine. Yes the ATC will capture the progress. When I took a 1 day crevasse course with RMI a few years ago they showed this way and we practiced both this and a carabiner with prussik. The only negative I can think of is if you needed to rappel down to get to the patient for some reason and you just used your ATC up top.

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I disagree with Marlin.

 

The mechanics of it will, in fact, work, but the forces are generally not considered acceptable. It will be hard to nearly impossible to haul up a victim going through an ATC (or similar) in guide mode without generating excessive forces on the anchor (by needing to add mechanical advantage).

 

The only way I have been taught, read, and teach is the progress capture pulley or a prussik.

 

Your concern of needing to rappel should also be a non-issue because you can always rappel with a munter.

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it does in fact work, but it's damned inefficient. If you're looking to save weight/complexity, bite the bullet and buy a microtraxion - a progress-capture pulley that also works as an ascender if you happen to be the one in the hole. I wouldn't normally buy/recommend a hundred-dollar pulley, but Petzl microtraxion is one that might even be worth paying retail. Mine lives on my harness, and sees more use than I ever expected before I started carrying it.

-Haireball

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Posted (edited)

CT Roll N Lock is pretty light and quite functional. I got one recently and use it for many rope access tasks. ATC would be terrible for this use, super inefficient as previously stated.

 

 

CT Roll N Lock

Edited by hanman

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I agree with the fact that an ATC will have a lot of friction and be inefficient in comparison to a pulley. However when compared to a single carabiner I think it would be a similar amount of inefficiency (although an experimental test with a dynamometer would be interesting to me to compare).

 

I have done a bunch of testing using a variety of carabiners in a 3:1 system instead of pulley and measuring their efficiency. The pulley I tested came in around 93% efficiency as compared to a true theoretically 3:1 system. The carabiners all ranged from 65% to 72% depending on how fat the carabiner was. The fatter carabiners such as a Petzl Attache were the best. My theory is that an ATC with a fat carabiner would be somewhere in the 60-70% range as similar to the carabiners. Plenty happy to abandon my theory if actual tests prove otherwise.

 

Anyway the best solution as Haireball stated is to just use a Petzl microtraxion. It serves the function of a pulley with a progress capture very well and it lives on my harness when I am in glaciated terrain.

 

Hanman I have never seen the CT Roll N Lock but it looks light and nice. Is the locking mechanism more toothed like a Microtraxion or Tblock or is it more of a general rope grab pinch mechanism. BTW your link doesn't seem to work on my computer.

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Posted (edited)

The Roll N Lock has horizontal ribs, kind of like a micro/rescuescender but perhaps a bit sharper. They say it can engage webbing as well for an adjustable PAS which I though was somewhat interesting. Really light device.

 

Here's another link to try... Link

 

 

 

MH

Edited by hanman

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Here's another link to try... Link

 

 

MH

 

Link works fine this time. I like the looks of that. Interesting that it fits webbing too.

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I'm with you on the inefficiency due to increased friction, but a little confused on how that translates into increased force on the anchor. Is there something else about the system in not grasping? Just curious.

 

-matt

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My feeble minded understanding is that if you have to pull harder due to the increased friction, you're introducing more force on the anchor.

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